/Engine/Source/Runtime/GeometryCore/Public/GeometryTypes.h
EOperationValidationResult is meant to be returned by Validate() functions of Operation classes (eg like ExtrudeMesh, etc) to indicate whether the operation can be successfully applied.
namespace UE { namespace Geometry { enum EOperationValidationResult { Ok = 0, Failed_UnknownReason = 1, Failed_InvalidTopology = 2, } } }